1. Field of the Invention
The present invention is directed to a system for setting up so-called LOS (line of sight) radio links between mobile transmitting/receiving stations and other mobile or stationary transmitting/receiving stations with a predetermined operating area, and preferably in a frequency band above 1 GHz.
2. Description of the Prior Art
In the case of LOS radio links of the kind used partly in the frequency band above 30 MHz and predominantly in the frequency band above 1 GHz, there exist severe limitations for use in mobile transmitting/receiving stations. This is true since, with a change of location of the mobile stations, the respective field strength attenuation or transmission loss between the calling station and another mobile or stationary remote station is unknown.
To prevent overloading of a radiotelephone network, it has been known to continually determine the number of mobile radiotelephones present in a radio cell, while the association of the radiotelephone to neighboring radio cells is also determined in accordance with the geographical and topographical conditions of the respective sub-area (DE 3,441,722). In this connection, it has also been known to monitor continually the transmission performance of the radio link and to take it into account for control of a dynamic cell size.
For mobile radio links, it has also been known to determine the radio zone boundary between two neighboring radio zones by measuring the relative distance between a mobile subscriber and fixed stations (radio concentrators) (DE 3,335,128). Also, a radio system has been known in which the intercommunicating radio stations adjust the transmitter power of the respective other station in response to the transmission performance (DE 3,417,233). For a radio network comprising a plurality of mobile stations it has also been known to have each station act as a relay between mobile stations communicating in pairs (DE 3,337,648). Finally, it has been known with mobile radio links to perform field strength measurements so as to obtain a criterion for switching a mobile subscriber from one radio area to the next (DE 3,012,484).
These known techniques are unsuitable for setting up optimum LOS radio links and for solving the problems arising in this connection.